1. Field of the Invention
This invention relates generally to semiconductor processing, and more particularly, to a method and apparatus for determining chemical mechanical polishing (CMP) pad conditioner effectiveness.
2. Description of the Related Art
CMP is a widely used means of planarizing silicon dioxide as well as other types of processing layers on semiconductor wafers. Chemical mechanical polishing typically utilizes an abrasive slurry disbursed in an alkaline or acidic solution to planarize the surface of the wafer through a combination of mechanical and chemical action. Generally, a chemical mechanical polishing tool includes a polishing device positioned above a rotatable circular platen or table on which a polishing pad is mounted. The polishing device may include one or more rotating carrier heads to which wafers may be secured, typically through the use of vacuum pressure. In use, the platen may be rotated and an abrasive slurry may be disbursed onto the polishing pad. Once the slurry has been applied to the polishing pad, a downward force may be applied to each rotating carrier head to press the attached wafer against the polishing pad. As the wafer is pressed against the polishing pad, the surface of the wafer is mechanically and chemically polished.
During a polishing process, material may be abraded away from the surface of a wafer and deposited on the surface of the polishing pad. The build up of waste material on the surface of the polishing pad is commonly referred to as glazing. Glazing may, among other things, degrade the porosity of the polishing pad reducing the flow of slurry to the polishing process, thus, reducing the effectiveness of the polishing pad. Those skilled in the art will appreciate that a conditioning wheel may be used during a conditioning process to abrade the surface of a polishing pad (i.e., the conditioning wheel may be used during a conditioning process to remove the waste material and other debris from the surface of the polishing pad.)
As semiconductor devices are scaled down, the importance of chemical mechanical polishing to the fabrication process increases. In particular, it becomes increasingly important to control and determine CMP pad conditioner effectiveness (i.e., determining how well the conditioning wheel is conditioning the polishing pad.) For example, after extended use, a conditioning wheel may become worn and incapable of properly conditioning the polishing pad. When this occurs, if undetected, wafers may be polished with an undesirably conditioned polishing pad.
Generally, a variety of known techniques may be used to determine CMP pad conditioner effectiveness. One method comprises monitoring the polish removal rate of the polishing pad. For example, by measuring the pre-polish thickness and the post-polish thickness of a process layer of a wafer, the polish removal rate of the polishing pad may be determined. Typically, with this method, a decrease in the polish removal rate of the polishing pad may be used to signal a decrease in CMP pad conditioner effectiveness.
In addition to polish removal rate, post-polish non-uniformity of a wafer may be used to determine CMP pad conditioner effectiveness. Generally, the post-polish non-uniformity of a wafer increases as the conditioning wheel becomes worn and is in need of replacing. For example, after extended use, the conditioning wheel may inadequately condition portions of the polishing pad, and the inadequately conditioned portions of the polishing pad may increase the surface non-uniformity of subsequently polished wafers.
Another method of determining CMP pad conditioner effectiveness comprises measuring the thickness of the polishing pad after a predetermined amount of conditioning time. For example, the post-conditioned thickness of the polishing pad may be compared with the pre-conditioned thickness to determine the xe2x80x9ccut ratexe2x80x9d of the conditioning process. Those skilled in the art will appreciate that a decrease in the cut rate of the conditioning process may be used to signal a decrease in the CMP pad conditioner effectiveness.
The existing methods of determining CMP pad conditioner effectiveness, however, suffer from several shortcomings. For example, with the existing techniques, the conditioning wheel may be used to condition a polishing pad until the polish removal rate declines or the surface non-uniformity of polished wafers increases. When this occurs, because of the degraded polishing process, wafers that were polished with the improperly conditioned polishing pad may have to be reworked, which may add significant time and cost to the semiconductor manufacturing process. In addition, when measuring cut rate of a conditioning process, the polishing tool is typically removed from production, thus, decreasing throughput of the manufacturing process.
The present invention is directed to overcoming, or at least reducing the effects of, one or more of the problems set forth above.
In one aspect of the present invention, a method is provided. The method includes supplying a signal to rotationally drive a conditioning wheel of a conditioning tool. A polishing pad of a polishing tool is conditioned using the rotationally driven conditioning wheel. Changes in the signal driving the conditioning wheel during the conditioning process are monitored. A conditioning effectiveness of the conditioning wheel is determined based on the changes observed in the monitored signal.
In another aspect of the present invention, a system is provided. The system includes a conditioning tool and a controller. The conditioning tool is adapted to condition a polishing pad of a polishing tool. The controller is coupled to at least one of the polishing tool or the conditioning tool. The controller is adapted to supply a signal to rotationally drive a conditioning wheel of the conditioning tool, monitor changes in the signal driving the conditioning wheel during a conditioning process, and determine a conditioning effectiveness of the conditioning wheel based on changes observed in the monitored signal.